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| 2. |
- Höglund, Erik, et al.
(författare)
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Suppression of aggressive behaviour in juvenile Atlantic cod (Gadus morhua) by L-tryptophan supplementation
- 2005
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Ingår i: AQUACULTURE. ; 249:1-4, s. 525-531
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Tidskriftsartikel (refereegranskat)abstract
- Aggressive interactions and cannibalism of juvenile Atlantic cod may cause substantial production losses under conditions of intensive rearing. In other teleosts, chronically increased brain concentrations and turnover of the neurotransmitter serotonin (5-hydroxytryptamine, 5-HT) are associated with suppressed aggression. Further, dietary supplementation with the serotonin precursor, L-tryptophan (TRP) suppresses aggression in juvenile rainbow trout (Onchorhyncus mykiss) and reduces cannibalism in juvenile grouper (Epinephelus coioides). In the present study, the behavioural effect of dietary TRP supplementation was observed in pairs of juvenile Atlantic cod subjected to repeated encounters for 10 days. After 3 days, one group was given TRP-supplemented feed (28 g/kg). A significant (P < 0.01) decrease in aggressive acts (from 40 +/- 2.7/ 10 min to 17 +/- 2.0/10 min, mean +/- standard error of mean) was seen after changing to TRP-supplemented feed. The mean number of aggressive acts was also significantly (P<0.05) lower in the TRP-treated group (17 +/- 2.0/10 min) compared to a control group not receiving TRP treatment (29 3.3/10 min). A second experiment examined the effect of TRP-supplemented feed (28 g/kg) on the activity of central 5-HT, quantified as the concentration ratio between the 5-HT metabolite, 5-hydroxyindoleacetic acid (5-HIAA), and 5-HT. In this experiment, the TRP-treated group ([5-HIAA]/[5-HT]=0.56 +/- 0.04) showed elevated values (P<0.038) compared with the control group ([5-HIAA]/[5-HT]=0.43 +/- 0.03). In conclusion, this study shows that juvenile Atlantic cod are highly aggressive and that supplementing the feed with TRP affects central 5-HT signalling systems and reduces this behaviour. (c) 2005 Elsevier B.V. All rights reserved.
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| 3. |
- Höglund, Erik, et al.
(författare)
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Tryptophan Metabolic Pathways and Brain Serotonergic Activity : A Comparative Review
- 2019
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Ingår i: Frontiers in Endocrinology. - : FRONTIERS MEDIA SA. - 1664-2392. ; 10
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Forskningsöversikt (refereegranskat)abstract
- The essential amino acid L-tryptophan (Trp) is the precursor of the monoaminergic neurotransmitter serotonin (5-hydroxytryptamine, 5-HT). Numerous studies have shown that elevated dietary Trp has a suppressive effect on aggressive behavior and post-stress plasma cortisol concentrations in vertebrates, including teleosts. These effects are believed to be mediated by the brain serotonergic system, even though all mechanisms involved are not well understood. The rate of 5-HT biosynthesis is limited by Trp availability, but only in neurons of the hindbrain raphe area predominantly expressing the isoform TPH2 of the enzyme tryptophan hydroxylase (TPH). In the periphery as well as in brain areas expressing TPH1, 5-HT synthesis is probably not restricted by Trp availability. Moreover, there are factors affecting Trp influx to the brain. Among those are acute stress, which, in contrast to long-term stress, may result in an increase in brain Trp availability. The mechanisms behind this stress induced increase in brain Trp concentration are not fully understood but sympathetic activation is likely to play an important role. Studies in mammals show that only a minor fraction of Trp is utilized for 5-HT synthesis whereas a larger fraction of the Trp pool enters the kynurenic pathway. The first stage of this pathway is catalyzed by the hepatic enzyme tryptophan 2,3-dioxygenase (TDO) and the extrahepatic enzyme indoleamine 2,3-dioxygenase (IDO), enzymes that are induced by glucocorticoids and pro-inflammatory cytokines, respectively. Thus, chronic stress and infections can shunt available Trp toward the kynurenic pathway and thereby lower 5-HT synthesis. In accordance with this, dietary fatty acids affecting the pro-inflammatory cytokines has been suggested to affect metabolic fate of Trp. While TDO seems to be conserved by evolution in the vertebrate linage, earlier studies suggested that IDO was only present mammals. However, recent phylogenic studies show that IDO paralogues are present within the whole vertebrate linage, however, their involvement in the immune and stress reaction in teleost fishes remains to be investigated. In this review we summarize the results from previous studies on the effects of dietary Trp supplementation on behavior and neuroendocrinology, focusing on possible mechanisms involved in mediating these effects.
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| 5. |
- Vindas, Marco A., et al.
(författare)
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Brain cortisol receptor expression differs in Arctic charr displaying opposite coping styles
- 2017
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Ingår i: Physiology and Behavior. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0031-9384 .- 1873-507X. ; 177, s. 161-168
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Tidskriftsartikel (refereegranskat)abstract
- Individually consistent behavioral and physiological responses to stressful situations (often referred to as coping styles) has been reported in many animal species. Differences in hypothalamic-pituitary axis reactivity characterize individuals, and it has been proposed that the glucocorticoid (gr) and mineralocorticoid (mr) receptors are fundamental in regulating coping styles. We sorted individuals into reactive and proactive coping styles by collapsing behavioral outputs from net restraint and confinement stress tests in a principal component analysis. We then analyzed plasma cortisol levels, serotonin neurochemistry and the relative mRNA expression of gr1 and mr in stressed individuals per coping style. Proactive fish were characterized as having a lower serotonergic activity and being more active under stress. In addition, proactive fish had higher hypothalamic gr1 and mr abundance and a higher mr/gr1 ratio, compared to reactive fish. We found no significant differences in cortisol or telencephalic mRNA, gr1 and mr expression, or their ratio. Brain MR and GR have been proven to have an important role in the appraisal, coping and adaptation to stressful stimuli, so that a higher expression of these receptors in proactive fish suggests increased tolerance and performance under stress, compared to reactive individuals. We present evidence of a conserved neuroendocrine mechanism associated with coping styles in a fish species which is ecologically very diverse and considered to be the most cold-adapted fish in freshwater. We propose that this may be a first step into exploiting this model in order to better understand climate-change related effects in sub populations and ecophenotypes.
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| 8. |
- Överli, Öyvind, et al.
(författare)
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Behavioral and neuroendocrine correlates of selection for stress responsiveness in rainbow trout - a review
- 2005
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Ingår i: INTEGRATIVE AND COMPARATIVE BIOLOGY. ; 45:3, s. 463-474
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Tidskriftsartikel (refereegranskat)abstract
- In rainbow trout the magnitude of the cortisol response to stress shows both consistency over time and a moderate to high degree of heritability, and high responding (HR) and low responding (LR) lines of rainbow trout have been generated by individual selection for consistently high or low post-stress cortisol values. Using 2nd and 3rd generation fish, we tested the hypothesis that differential stress responsiveness is associated with behavioral alterations in the HR-LR trout model. LR fish showed a tendency to become socially dominant, a rapid recovery of food intake after transfer to a novel environment, and a reduced locomotor response in a territorial intrusion test. Furthermore, stress induced elevation of brain stem and optic tectum concentrations of the monoamine neurotransmitters serotonin, dopamine, and norepinephrine and their metabolites suggests that both synthesis and metabolism of these transmitters were elevated after stress to a larger degree in HR than in LR trout. A divergent pattern was seen in the hypothalamus, where LR fish displayed elevated levels of 5-hydroxyindoleacetic acid (a serotonin metabolite) and 3-methoxy-4-hydroxyphenylglycol (a norepinephrine metabolite). Thus, selection for a single trait, cortisol responsiveness, in rainbow trout is associated with concurrent changes in both behavior and central signaling systems. The apparent parallel to genetically determined stress coping styles in mammals, and the existence of similar trait associations in unselected populations of rainbow trout, suggests an evolutionarily conserved correlation between multiple traits. Continuing studies on the HR and LR trout lines are aimed at providing the physiological and genetic basis for new marker-assisted selection strategies in the rapidly developing finfish aquaculture industry, as well as increased knowledge of the function and evolution of central neuroendocrine signaling systems.
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| 9. |
- Øverli, Øyvind
(författare)
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Behavioural and Neuroendocrine Effects of Stress in Salmonid Fish
- 2001
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Stress can affect several behavioural patterns, such as food intake and the general activity level of an animal. The central monoamine neurotransmitters serotonin, dopamine, and norepinephrine are important in the mediation of both behavioural and neuroendocrine stress effects. This thesis describes studies of two salmonid fish model systems: Fish that become socially dominant or subordinate when reared in pairs, and rainbow trout (Oncorhynchus mykiss) genetically selected for high (HR) and low (LR) stress responsiveness, in terms of stress induced cortisol release. Socially subordinate individuals are often subject to chronic stress, and it was found that plasma cortisol and brain monoaminergic activity rapidly increased in subordinate fish during the initial 24 h period following fights for social dominance in pairs of rainbow trout. In pairs of Arctic char (Salvelinus alpinus), subordinate individuals were characterised by an inhibition of food intake and aggression, and low spontaneous locomotion. Appetite inhibition in subordinate fish was reversed by subsequent rearing in isolation, and this effect was probably related to a concomitant decrease in brain serotonergic activity. Furthermore, differential stress responsiveness in HR and LR rainbow trout was associated with differences in behaviour, as well as changes in brain monoaminergic activity. HR fish displayed higher locomotor activity when challenged by a conspecific intruder. This response was probably related to a larger stress induced activation of brain dopaminergic systems in these fish. Finally it was shown that the steroid 'stress-hormone' cortisol has dose- and context-dependent behavioural effects in fish, as has been described in mammals. Specifically, short- term cortisol treatment elevated the behavioural response to a territorial intruder, while long-term treatment, like chronic stress, had the opposite effect, inhibiting locomotor activity and aggression. It is concluded that the signalling systems involved in behavioural and neuroendocrine control during stress display extensive similarities between teleost fishes and mammals.
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